Global satellite navigation fulfills pervasive needs. Initially a service for military and general aviation, Global Navigation Satellite Services (GNSS) are expanding into many commercial and consumer products for applications ranging from casual to emergency services. More recently cellular phones have been developed that provide location based service applications and, in response to government requirements, emergency caller location services. The preponderance of these services is enabled by the US Air Force managed Global Positioning System (GPS). GPS is now or may soon be joined by several additional GNSS systems including: Glonass (Russia), Galileo (European Space Agency) and QZSS (Japan). Cellular phone embedded GPS uses the cellular network as an assistance tool to forward current and predicted satellite orbital parameter data to reduce the satellite signal search burden. This is useful in ordinary phones that are equipped with chip-scale GPS receivers that can use other signal processing, RF and computational processing elements already inside these phones. The assistance method provides a substantial reduction in the time to initially acquire a position fix by reducing the search field and by limiting the search to where the overhead satellites are known to occupy distinct frequency and code-phase zones of the signal search area. Mobile assisted GPS is the backbone of positioning devices for Emergency 9-1-1 (E911) calls in the United States, and in 2005 supported an estimated time-urgent 100 million E911 calls.
The utility of exact positioning cannot be overestimated when safety and security is involved, and several governments now seek precise location for their respective countries' public communication and first-responder infrastructure. At the same time that they seek this service, their public communication infrastructure is shifting rapidly from fixed circuit switched networks to Voice Over Internet Protocol (VoIP) networks. However, current IP networks are not geo-referenced to either intelligently route or pinpoint the location of E911 callers. Further, VoIP is a service that has portable or nomadic connectivity. VoIP service providers are also no longer 100% facilities based providers. Therefore, VoIP is often hosted, that is supported technically, across facilities with no linkage administratively between the facility or access and the VoIP service providers. Additionally, no single current provider has a network plant with a reach of VoIP service that covers all the geographical points at which VoIP subscribers connect.
To support the ability to locate the VoIP-enabled emergency caller, proposals have been offered to manually survey or map the underlying fixed plant assets. This method may have limited effectiveness, would require service suspension if the user connects at a new location, and would incur additional mapping costs when the user connects at a new location. Other proposals to use parasitic methods by acquiring and mapping signals such as WiFi or TV broadcast signals. Some have proposed entirely new, dedicated signals, using separate spectrum and infrastructure, deployed for the sole purpose of locating objects, pets or people. A common belief or premise of these proposals is GPS cannot operate successfully to reach receiver points located inside buildings and homes due to limits of effective satellite signal sensitivity. This limitation is often attributed to the fact that the satellites are far away and have comparatively limited transmission power.